* Re: [gentoo-user] Re: Cannot compile texinfo: Illegal instruction -> Wrong -march and -mtune flags?
@ 2007-08-03 1:06 99% ` Daniel da Veiga
0 siblings, 0 replies; 1+ results
From: Daniel da Veiga @ 2007-08-03 1:06 UTC (permalink / raw
To: gentoo-user
On 8/2/07, Florian Philipp <f.philipp@addcom.de> wrote:
> Am Donnerstag 02 August 2007 23:36 schrieb Alexander Skwar:
> > · Florian Philipp <f.philipp@addcom.de>:
> > > You see, they are not compatible and even if some code works I wouldn't
> > > bet multimedia apps will perform well.
> > >
> > > With -mtune the instruction set stays the same. It is just "rearranged".
> >
> > Hm. Allright. When using just -mtune (ie. without -march), the
> > docs at
> > http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/i386-and-x86_002d64-Options.htm
> >l
> >
> > say:
> > | While picking a specific cpu-type will schedule things appropriately
> > | for that particular chip, the compiler will not generate any code that
> > | does not run on the i386 without the -march=cpu-type option being used.
> >
> > If -mtune=athlon-xp is used, code is generated which may make
> > use of 3dNOW!. 3dNOW! is, of course, not to be found on 386 :)
> > If the instruction set stays the same, code generated with
> > -mtune=athlon-xp would not be executable on 386 machines, if
> > I understand you correctly.
> >
> > Hm. With -mtune, the set of available instructions (ie.
> > stuff like 3dNOW!, I suppose?) is NOT changed from the default
> > of i386, is it? Or what does "Tune to cpu-type everything applicable
> > about the generated code, except for the ABI and the set of available
> > instructions." mean - especially note the "except for [...] the set of
> > available instructions" part.
> >
> > So with "-mtune=pentium-m -march=athlon-xp" I'm making the compiler
> > generate code which is "ordered" the way it's best for pentium-m
> > machines while allowing it to use athlon-xp instruction set? Is
> > that what I'm doing?
> >
> > If so, then it seems you're right - code will run, but maybe not
> > so well.
> >
> > Is that understanding correct? If so, then I really should think
> > twice about using "-mtune=pentium-m -march=athlon-xp", shouldn't
> > I?
> >
> > Curious,
> >
> > Alexander Skwar
> > --
>
> At least that's how I understand the issue. At the moment I've got two ideas
> to solve your problem:
>
> 1. set march to an inferior target (pentium-3 and pentium-3m seem okay: mmx
> and sse) and mtune for one (or even both?) of them
> 2. set march to one of them and disable incompatible instruction sets with
> options like -mno-sse2 or -mno-3dnow
>
>
Isn't the -march=i686 valid?
I guess that would be the most "compatible" option for binaries that
will run on AMD and Intel processors... Or simply use no "-march"
setting, only "-mtune"... I did that recently to switch a whole system
from an Athlon XP to a Intel Core Duo...
--
Daniel da Veiga
Computer Operator - RS - Brazil
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2007-08-02 18:15 [gentoo-user] Cannot compile texinfo: Illegal instruction -> Wrong -march and -mtune flags? Alexander Skwar
2007-08-02 20:31 ` [gentoo-user] " Florian Philipp
2007-08-02 21:36 ` Alexander Skwar
2007-08-02 22:07 ` Florian Philipp
2007-08-03 1:06 99% ` Daniel da Veiga
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